Neutron detectors are an instance of element technology that supports various kinds of neutron-based technology. Neutron detectors of ever higher performance are required in order to cope with developments in a variety of neutron-based technology, for instance in the field of security, for instance in cargo inspection, in the field of industrial non-destructive testing, or in the field of academic research, for instance structural analysis by neutron diffraction.
The main performance items required from neutron detectors are neutron detection efficiency, and discrimination between neutrons and γ-rays (hereafter also referred to as n/γ discrimination). Detection efficiency refers herein to the ratio of the amount of neutrons that are detected by a detector with respect to the amount of neutrons that are emitted by a neutron source and that strike the detector. Further, n/γ discrimination denotes the ratio of a neutron detection signal with respect to background noise derived from γ-rays. Herein, γ-rays are generated when neutrons strike an element such as Fe (iron), Pb (lead), Cd (cadmium), C (carbon), N (nitrogen) or the like contained in an object to be inspected or in a constituent member for neutron detection. If n/γ discrimination is low, a signal that fails to reflect the interactions between neutrons and the object to be inspected is mixed thereby increasing so-called background noise accordingly.
Neutrons have a high ability of passing through a substance without interacting with the latter, and hence neutron rays are ordinarily detected by relying on neutron capture reactions in which neutrons are quickly converted to energetic charged particles. Conventionally known 3He detectors, for instance, rely on a neutron capture reaction by the 3He isotope, in which neutrons are detected through conversion to protons and tritons, which are energetic charged particles. Such a detector exhibits high detection efficiency, and is excellent in n/γ discrimination, but 3He is an extremely expensive substance, and resources are becoming depleted in recent years, all of which is problematic (see Non-Patent Document 1).
Detectors that utilize a scintillator for neutrons have been developed recently as alternatives for the abovementioned 3He detectors. A scintillator for neutrons denotes herein a substance that emits light when struck by neutrons. The various performance items of a neutron detector that utilizes such a scintillator depend on the substance that makes up the scintillator. For instance, the detection efficiency of the scintillator towards neutrons depends on the content of isotope that is susceptible to a neutron capture reaction. Further, the n/γ discrimination depends on the density and the effective atomic number of the scintillator. The probability of interactions with γ-rays decreases, and background noise derived from γ-rays can be reduced, if the density and the effective atomic number of the scintillator are small.
To date, 6Li-containing glass and plastic fibers covered with 6Li and ZnS(Ag) have been developed as scintillators for neutrons, but the foregoing have still room for improvement as regards neutron detection efficiency and n/γ discrimination (see Non-Patent Document 1).